package ru.cod.rs.x1000;

import java.io.PrintWriter;
import java.util.Scanner;

public class Z1820 {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		PrintWriter out = new PrintWriter(System.out);

		int a = in.nextInt();
		int b = in.nextInt();
		out.println(fact(a * 2) / fact(a * 2 - b));
		out.flush();
	}

	public static long fact(int a) {
		long result = 1;
		for (int i = 1; i <= a; i++) {
			result *= i;
		}
		return result;
	}
}
